Two thin lenses of focal length `f_(1)` and `f_(2)` are in contact and coaxial. The power of the combination is

Two thin convex lenses of focal lengths f_(1) and f_(2) are in contact and coaxial. The power of the combination is

Two thin lenses of focal lengths f1 and f2, are in contact and coaxial. The power of combination is

Two lenses of focal legths f_(1) and f_(2) are kept in contact coaxially. The resultant power of combination willl be

Two thin lenses of focal lengths f_(1) and f_(2) are in contact. The focal length of this combination is

Two thin lenses of focal lengths f_(1) and f_(2) are in contact. The focal length of this combination is

Two thin lenses of focal lengths f_(1) and f_(2) are in contact. The focal length of this combination is

Two thin convex lenses of focal length f_1 and f_2 are kept in contact. The power of the combination is